Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Wide band needs of modern communication applications on airborne and ground platforms at high frequency (HF), very high frequency (VHF), and ultra-high frequency (UHF) bands result in desired antenna specifications such as high forward gain, low cross-polarization, low back lobe radiation, compact size, and low cost. Some widely used SATCOM antennas in the UHF band include, for example, the eggbeater antenna including two cross circular loop antennas coupled to a hybrid quadrature coupler.
In Radio Frequency Identification (RFID) mobile applications, an RFID reader antenna needs to have high performance including a broadband operation, circular polarization, and a large angular coverage from horizon to zenith. For systems at RFID frequencies (e.g., 900 MHz range), wavelength may be on the order of one third to one quarter of a meter and conventional antennas may be physically too large for commercial use. In GPS applications, antennas need to have precise narrow band performance at specific frequency bands (e.g., L1 and L2 bands).